Thanks to Opensnitch, I noticed tucnak try to connect to tucnak.vaiz.cz
on startup.  I would very much like such 'dial home' behaviour to be
disabled by default, and only be enabled after a opt-in user selection.

I am not sure which code path is involved, but see the DNS name listed
in three source files:

% grep -rl tucnak.vaiz.cz .
./src/update.c
./src/ac.c
./src/rain.c
%